Invoicing of invoicing unit (account &1) terminated

What causes this issue?

Invoicing of the invoicing unit (grouping of documents to be invoiced
in the system) for the specified account could not be performed
correctly.
The reasons can be found in the previous lines of the log.
You can find a list of documents which form the corresponding invoicing
unit at the end.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Look at the previous lines of the log and correct the errors specified
there.
You can find further notes in the long texts of the individual error
messages.

Error message extract from SAP system. Copyright SAP SE.